It is known in the art to use complexes of Pd(II) as homogeneous catalysts for the carbonylation of olefins. Generally these processes require a comparatively high pressure of carbon monoxide with a consequent need for expensive equipment.
A general review of the carbonylation of olefins using palladium complexes as catalysts appears in Angew, Chem. 80, 352, (1968) (International Edition, Vol. 7 (1968), p. 329) and references therein.
There is disclosed in U.S. Pat. No. 3,437,676 a process for the carbonylation of olefinically unsaturated compounds to form products selected from the group consisting of carboxylic acids and esters by reacting an olefinically unsaturated compound with carbon monoxide and with a hydroxy compound selected from the group consisting of water, alcohols and phenols in the presence of a catalyst, the improvement comprising employing a specific amount of a complex palladium salt having the formula L.sub.m PdX.sub.n in which L denotes a member selected from the group consisting of organic phosphines, organic phosphites, ammonia, amines, nitriles and unsaturated hydrocarbons, X denotes an acid equivalent selected from the group consisting of chloride, bromide, sulfate, phosphate, acetate, nitrate, propionate and borate, m denotes an integer of from 1 to 4 and n denotes either the number 1 or 2.
U.S. Pat. No. 3,887,595 to Nozaki discloses a process of carbonylating olefinically unsaturated hydrocarbons of from 2 to 30 carbons, not including acetylenic or conjugated olefinic unsaturation, with carbon monoxide and at least one hydroxylic compound selected from the group consisting of water, alkanol and carboxylic acid in the presence of a catalyst consisting essentially of a zerovalent noble metal phosphine complex of the general formula (R.sub.3 P).sub.n M, wherein M is palladium or platinum, the improvement comprising producing predominately straight chain products.
In U.S. Pat. No. 3,919,272 there is disclosed a catalytic process for preparing linear saturated carboxylic products from alpha olefins having 3 to 40 carbon atoms by a process of heating alpha olefins with a PdCl.sub.2 [As(C.sub.6 H.sub.5).sub.3 ].sub.2 --GeCl.sub.2 catalyst.
U.S. Pat. No. 3,952,034 discloses a process for carbonylation of olefins and acetylenes to a carboxylic acid or ester using a homogenous catalyst system comprising palladium together with iron or a metal of groups IVA, VA or IIIB, the catalyst being either a polynuclear complex incorporating both metals or a mixture of a soluble palladium salt and metal halide.
In EPA No. 0 055 875 an essentially halide-free palladium catalyst containing a triorganophosphine, in the absence of sodium acetate, is used for the carbonylation of an olefin.
European patent application No. 0 106 379 discloses a process for the carbonylation of olefinically unsaturated compounds with a palladium catalyst wherein the catalyst also contains at least 5 moles of phosphine and three aryl groups per gram atom of palladium.
None of the references in the prior art appears to address the specific problems of dicarbonylating non-conjugated, alpha, omega-aliphatic linear dienes, such as 1,7-octadiene, to produce linear aliphatic dicarboxylic acids and their derivatives. Further, in some of the catalyst systems there is a problem with metal plating and precipitation.
It would be an advance in the art to devise a catalyst system for producing aliphatic dicarboxylic acids in improved yield with an improved yield of desired linear aliphatic dicarboxylic acids. A palladium catalyst which could be recovered without usual amounts of metal plating and precipitation would also be an improvement: a palladium catalyst which exhibited improved solubilization under ambient conditions would be a further improvement over the art.
The product aliphatic diacids would be useful as corrosion inhibitors for antifreeze. The product diacids are comparable to sebacic acid, a commercial corrosion inhibitor. The product diacids should be less expensive than the sebacic acid.